Hi.
I always missed a "reverse" value for the animation-direction property.
Sometimes you have a complex animation that will be applied to two different elements, but one of them should be in reverse. It just feels silly copying the whole animation and reversing the percentages to get the desired effect. So, a value named "reverse" would define that, for that rule, the animation should always run on reverse mode, from 100% to 0%.
ps: I'm sorry if this is a recurrent theme, but I couldn't find any result searching the list archives.
Regards,
Gabriel Gilini